The present invention relates to a direct current motor, and more particularly to such a direct current motor having a plurality of armature windings disposed around a disc-shaped or cylindrical coreless armature.
Conventionally, a number of motors of the type with an armature core having a plurality of armature windings formed in a lap winding or wave winding manner are widely used. However, when the conventional armature windings are employed in the coreless type motor, various shortcomings are encountered as will be explained by referring to FIG. 1. FIG. 1 is a developed view of known armature windings formed in a lap winding manner and employed in a coreless motor, the lap winding armature comprising twenty four armature coils, provided with a field magnet with eight magnetic poles. The field magnet 1 has magnetic poles 1-1, 1-2, . . . , 1-8, magnetized alternately to N and S with 45 degree angular intervals. A commutator 3 comprises commutator segments 3-1, 3-2, . . . , 3-24, with 15 degree angular intervals (1/3 the magnetic pole width), and every four commutator segments which are angularly spaced 90 degrees (2/1 the magnetic pole width) from each other are electrically connected to each other by conductors serving as short-circuitting members. More specifically, commutator segments 3-1, 3-7, 3-13, and 3-19, commutator segments 3-2, 3-8, 3-14, and 3-20, commutator segments 3-3, 3-9, 3-15, and 3-21, commutator segments 3-4, 3-10, 3-16, and 3-22, commutator segments 3-5, 3-11, 3-17, and 3-23, and commutator segments 3-6, 3-12, 3-18, and 3-24 are inter-connected or short-circuitted. An armature 2 is an open-connected normal lap winding, with the angular intervals of the conductors which contribute to the generation of torque in each armature coil being set equal to the magnetic pole width. Armature coils 2-1, 2-2, . . . , 2-24 are each disposed with an equal pitch of an angular interval of 15 degrees (1/3 the magnetic pole pitch), and are superimposed on each other. Each armature coil is subjected to lap winding connection. The connecting portions of the armature coils 2-1 and 2-2, the armature coils 2-2 and 2-3, the armature coils 2-3 and 2-4, . . . , the armature coils 2-23 and 2-24, and the armature coils 2-24 and 2-1 are connected respectively to the commutator segments 3-2, 3-3, 3-4, . . . , 3-24, 3-1. To brushes 4-1 and 4-2 is supplied power from D.C. power source positive and negative poles 5-1 and 5-2, respectively. The brushes 4-1 and 4-2 are slidable on the commutator segments are disposed with 135 degree angular intervals (3/1 the magnetic pole width), but may equivalently be disposed with either 45 degree angular intervals (the magnetic pole width), 225 degree angular intervals (5/1 the magnetic pole width), or 315 degree angular intervals (7/1 the magnetic pole width). It is apparent that use of brushes 4-1, 4-2, . . . , 4-8 as shown by the broken lines dispenses with short-circuitting of the commutator segments. More specifically, the brushes 4-1, 4-3, 4-5, and 4-7 are supplied with an electric current from the D.C. power source positive terminal 5-1, and the brushes 4-2, 4-4, 4-6, and 4-8 are supplied with an electric current from the D.C. power source negative terminal 5-2, the brushes being angularly spaced 45 degrees (the magnetic pole width). In the configuration as shown, an electric current flows in the direction of the arrowheads, and torque is generated in each armature coil, so that the armature 2 and the commutator 3 are respectively rotated in the directions of the arrows A and B, and work as a commutator motor. With such a motor, the armature coils are superimposed in multiple layers, resulting in an increased thickness of the armature. Such an increased thickness weakens an effective magnetic field passing through the armature, thus reducing the efficiency and starting torque of the motor. In order to eliminate those shortcomings, a prior art effort has been directed to decreasing the thickness of the conductor portions contributing to the generation of torque. However, this process for decreasing the thickness of the conductor portions is performed by press molding, and accordingly is often accompanied by such defects as breaking and short-circuitting of the armature coils. Further, since the phase relationship between the armature coils cannot be positively held in the desired state at the time the coils are arranged, a correct phase relationship between the windings is liable to be distorted, and hence a highly efficient direct current motor has been difficult to fabricate. Accordingly, prior art DC motors are costly and cannot be mass-produced.
The foregoing shortcomings could be overcome by reducing the number of armature coils. Such a proposal however would be disadvantageous in that with a smaller number of armature coils, the number of switchings of an armature current per revolution of the armature relatively to the magnetic poles would be reduced, resulting in poor commutating characteristics. As a result, reverse torque is generated and the operation efficiency and starting torque would be reduced. Furthermore, since the number of armature coils present between the positive and negative terminals of the D.C. power supply is extremely small, the arrangement could not be used as a direct current motor for use with a high voltage. Sparking would frequently take place and short-circuitting troubles would be apt to occur. The motor would therefore be rendered less durable.
In conventional coreless motors with cylindrical armatures, insulated wires are one by one wound, by way of alignment winding, fully or partly obliquely with respect to the winding width, alternately folded over at both ends substantially through every 180 degrees, and successively coiled to provide the cylindrical armature without the wire ends being superimposed on each other in the winding width. These prior coreless motors, however, cannot be mass-produced and hence expensive to produce.